feat(go/M2.3+M2.4): port domain/fees.CalculateFee and CalculateJuniorFee

Ports calculate_fee and calculate_junior_fee from scripts/attendance.py
into a new go/internal/domain/fees package. Introduces the Expected type
(Value int, Unknown bool) for the junior "?" sentinel, keeping the Go
API strictly typed instead of mirroring Python's str|int return.

All 20 table-driven tests pass with -race; golangci-lint clean.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

CHANGELOG.md

@@ -1,5 +1,10 @@
 # Changelog
 
+## 2026-05-06 00:07 CEST — feat(go/M2.2): port czech.ParseMonthReferences
+
+- `internal/domain/czech.ParseMonthReferences`: three-pass regex (numeric slash, dot, Czech month names) with range wrap-around and `m≥10 → previousYear` heuristic, byte-equivalent to Python.
+- 35 table-driven tests; all expected outputs verified against live Python before locking (addresses risk #4 from the rewrite plan).
+
 ## 2026-05-05 23:33 CEST — feat(go/M2.1): port czech.Normalize
 
 - First M2 pure-domain task: `internal/domain/czech.Normalize` (NFKD + Mn-strip + lowercase), byte-equivalent to Python `czech_utils.normalize`.

CLAUDE.md

@@ -64,13 +64,13 @@ Fio Bank API               ──► sync_fio_to_sheets.py ──► Google Shee
 ### Member tiers
 
 Tiers are set in column B of the attendance sheet:
-- `A` — Adult, pays fees (750 CZK/month for 2+ sessions, 200 CZK for exactly 1)
+- `A` — Adult, pays fees (per-month rate from `ADULT_FEE_MONTHLY_RATE`, fallback 700 CZK for 2+ sessions; 200 CZK for exactly 1)
 - `J` — Junior attending adult practices; their attendance is merged with the junior sheet
 - `X` — Excluded from junior fee calculation (coaches, etc.)
 
 ### Fee calculation
 
-- Adults: 0 sessions → 0, 1 session → 200 CZK, 2+ sessions → monthly rate (default 750 CZK)
+- Adults: 0 sessions → 0, 1 session → 200 CZK, 2+ sessions → monthly rate (default 700 CZK)
 - Juniors: 0 → 0, 1 → `"?"` (manual review required), 2+ → monthly rate (default 500 CZK)
 - Per-member per-month overrides live in the `exceptions` tab of the payments sheet (columns: Name, Period YYYY-MM, Amount, Note). Exceptions are keyed by `(normalize(name), normalize(period))`.
 

docs/plans/2026-05-03-2349-go-backend-rewrite-progress.md

@@ -45,7 +45,7 @@ Goal: every pure function from the Python backend exists in Go with a parity tes
 Each task: port the function, write Go unit tests for fresh cases, hook into the Tier-1 parity runner.
 
 - [x] **M2.1** `domain/czech.Normalize` — port [czech_utils.py](scripts/czech_utils.py) `normalize` (NFKD + combining-mark strip + lowercase) — `20ade6d`
-- [ ] **M2.2** `domain/czech.ParseMonthReferences` — port `parse_month_references` (45 month declensions, range wrap, year inference)
+- [x] **M2.2** `domain/czech.ParseMonthReferences` — port `parse_month_references` (45 month declensions, range wrap, year inference) — `0a8017f`
 - [ ] **M2.3** `domain/fees.CalculateFee` — port [attendance.py](scripts/attendance.py) `calculate_fee` (constants table)
 - [ ] **M2.4** `domain/fees.CalculateJuniorFee` — port `calculate_junior_fee` with `Expected{Value int; Unknown bool}` for the `"?"` sentinel
 - [ ] **M2.5** `domain/money.ParseCZK` — port [infer_payments.py](scripts/infer_payments.py) `parse_czk_amount` (Czech locale: comma decimal, dot/space thousand separators)

go/internal/domain/fees/fees.go

@@ -0,0 +1,34 @@
+// Package fees ports fee calculation from scripts/attendance.py.
+package fees
+
+const (
+	AdultFeeDefault = 700 // CZK fallback for 2+ practices when month not in AdultFeeMonthlyRate
+	AdultFeeSingle  = 200 // CZK for exactly 1 practice
+)
+
+// AdultFeeMonthlyRate mirrors ADULT_FEE_MONTHLY_RATE in scripts/attendance.py.
+// Months absent from this map fall back to AdultFeeDefault.
+var AdultFeeMonthlyRate = map[string]int{
+	"2025-09": 750, "2025-10": 750, "2025-11": 750, "2025-12": 750,
+	"2026-01": 750, "2026-02": 750, "2026-03": 350,
+	"2026-04": 700, "2026-05": 700,
+}
+
+// CalculateFee returns the adult fee in CZK for attendanceCount practices in
+// the given monthKey (format "YYYY-MM").
+//
+//	0 practices → 0
+//	1 practice  → AdultFeeSingle (200)
+//	2+          → AdultFeeMonthlyRate[monthKey] or AdultFeeDefault
+func CalculateFee(attendanceCount int, monthKey string) int {
+	if attendanceCount == 0 {
+		return 0
+	}
+	if attendanceCount == 1 {
+		return AdultFeeSingle
+	}
+	if rate, ok := AdultFeeMonthlyRate[monthKey]; ok {
+		return rate
+	}
+	return AdultFeeDefault
+}

go/internal/domain/fees/fees_test.go

@@ -0,0 +1,37 @@
+package fees
+
+import "testing"
+
+func TestCalculateFee(t *testing.T) {
+	t.Parallel()
+
+	// All expected outputs verified against live Python implementation on 2026-05-06:
+	//   PYTHONPATH=scripts:. python -c 'from attendance import calculate_fee; print([calculate_fee(c,m) for c,m in [(0,"2026-05"),(0,""),(1,"2026-05"),(1,"unknown"),(2,"2026-05"),(2,"2026-03"),(2,"2025-09"),(5,"2026-05"),(2,"2027-01"),(2,"")]])'
+	tests := []struct {
+		name  string
+		count int
+		month string
+		want  int
+	}{
+		{"zero short-circuits", 0, "2026-05", 0},
+		{"zero empty month", 0, "", 0},
+		{"single practice", 1, "2026-05", 200},
+		{"single ignores monthKey", 1, "unknown", 200},
+		{"two practices configured month", 2, "2026-05", 700},
+		{"two practices reduced march", 2, "2026-03", 350},
+		{"two practices early season", 2, "2025-09", 750},
+		{"high count same as two", 5, "2026-05", 700},
+		{"unknown future month falls back", 2, "2027-01", 700},
+		{"empty month falls back", 2, "", 700},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+			got := CalculateFee(tc.count, tc.month)
+			if got != tc.want {
+				t.Errorf("CalculateFee(%d, %q) = %d, want %d", tc.count, tc.month, got, tc.want)
+			}
+		})
+	}
+}

go/internal/domain/fees/junior.go

@@ -0,0 +1,37 @@
+package fees
+
+const JuniorFeeDefault = 500 // CZK fallback for 2+ practices when month not in JuniorFeeMonthlyRate
+
+// JuniorFeeMonthlyRate mirrors JUNIOR_MONTHLY_RATE in scripts/attendance.py.
+// Months absent from this map fall back to JuniorFeeDefault.
+var JuniorFeeMonthlyRate = map[string]int{
+	"2025-09": 250,
+	"2026-03": 250,
+}
+
+// Expected is the result of a junior fee calculation.
+// When Unknown is true the fee requires manual review (Python returns "?");
+// in that case Value is meaningless — always check Unknown first.
+type Expected struct {
+	Value   int
+	Unknown bool
+}
+
+// CalculateJuniorFee returns the junior fee for attendanceCount practices in
+// the given monthKey (format "YYYY-MM").
+//
+//	0 practices → Expected{Value: 0}
+//	1 practice  → Expected{Unknown: true}  (manual review; Python sentinel "?")
+//	2+          → Expected{Value: JuniorFeeMonthlyRate[monthKey] or JuniorFeeDefault}
+func CalculateJuniorFee(attendanceCount int, monthKey string) Expected {
+	if attendanceCount == 0 {
+		return Expected{Value: 0}
+	}
+	if attendanceCount == 1 {
+		return Expected{Unknown: true}
+	}
+	if rate, ok := JuniorFeeMonthlyRate[monthKey]; ok {
+		return Expected{Value: rate}
+	}
+	return Expected{Value: JuniorFeeDefault}
+}

go/internal/domain/fees/junior_test.go

@@ -0,0 +1,37 @@
+package fees
+
+import "testing"
+
+func TestCalculateJuniorFee(t *testing.T) {
+	t.Parallel()
+
+	// All expected outputs verified against live Python implementation on 2026-05-06:
+	//   PYTHONPATH=scripts:. python -c 'from attendance import calculate_junior_fee; print([calculate_junior_fee(c,m) for c,m in [(0,"2026-05"),(0,""),(1,"2026-05"),(1,"unknown"),(2,"2026-05"),(2,"2025-09"),(2,"2026-03"),(5,"2025-09"),(2,"2027-01"),(2,"")]])'
+	tests := []struct {
+		name  string
+		count int
+		month string
+		want  Expected
+	}{
+		{"zero short-circuits", 0, "2026-05", Expected{Value: 0}},
+		{"zero empty month", 0, "", Expected{Value: 0}},
+		{"single practice sentinel", 1, "2026-05", Expected{Unknown: true}},
+		{"single ignores monthKey", 1, "unknown", Expected{Unknown: true}},
+		{"two practices default month", 2, "2026-05", Expected{Value: 500}},
+		{"two practices reduced sept", 2, "2025-09", Expected{Value: 250}},
+		{"two practices reduced march", 2, "2026-03", Expected{Value: 250}},
+		{"high count same as two", 5, "2025-09", Expected{Value: 250}},
+		{"unknown future month falls back", 2, "2027-01", Expected{Value: 500}},
+		{"empty month falls back", 2, "", Expected{Value: 500}},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+			got := CalculateJuniorFee(tc.count, tc.month)
+			if got != tc.want {
+				t.Errorf("CalculateJuniorFee(%d, %q) = %+v, want %+v", tc.count, tc.month, got, tc.want)
+			}
+		})
+	}
+}